1. Field of the Invention
The present invention relates to a memory, and particularly to an RRAM structure and a method of making the same.
2. Description of the Prior Art
Resistive random access memory (RRAM) is a new memory structure created in the semi-conductive field. An RRAM stores data by using the variable resistance characteristic of a dielectric layer interposed between two electrodes. Such dielectric layer, as a resistive layer, is normally insulating but can be made to be conductive through a filament or conduction path formed after application of a sufficiently high voltage, i.e. through a forming process. The conduction path formation can arise from different mechanisms, including defects, metal migration, etc. Once the filament is formed, it may be reset (i.e. broken, resulting in high resistance) or set (i.e. re-formed, resulting in lower resistance) by an appropriately applied voltage.
FIGS. 1 and 2 show a schematic cross-sectional view of a conventional RRAM at a low resistance status and a high resistance status, respectively. As shown in FIGS. 1 and 2, an RRAM 10 includes a bottom electrode 12, a resistive layer 14 and a top electrode 20. A forming process has been performed on the RRAM 10, during which a gradually increasing voltage is applied to the top electrode 20 and the bottom electrode 12, and then the current flowing through the bottom electrode 12, the resistive layer 14 and the top electrode 20 is raised to a compliance current. In this way, the quality of the resistive layer 14 becomes non-uniform and the upper part of the resistive layer 14 will have fewer defects than the lower part of the resistive layer 14. When the RRAM is working upon application of a voltage, current filament 22 occurs in the resistive layer 14. As shown in FIG. 1, the current filament 22 distributes from the bottom electrode 12 to the top electrode 20 to make the RRAM 10 have a low resistance. As shown in FIG. 2, the current filament 22 is broken at the upper portion of the resistive layer 14 to make the RRAM 10 have a high resistance.
The forming process mentioned above is highly complicated and time-consuming. Furthermore, the forming process is performed electrically through a random way, in which breakdown is easily out of control, resulting in low yield.
Therefore, there is still a need for a novel RRAM which can be made easily and has an excellent performance.